Dark Advisor

Convert, grovel (When this creature enters the battlefield, you may pay {x}. If you do, put X -1/-1 counters on it and X +1/+1 counters on target creature.)
When Dark Advisor enters the battlefield, put a corrupt counter on each creature it groveled to.
At the beginning of your upkeep, each creature with a corrupt counter on it deals 1 damage to its controller.